The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the treatment of the discs, cartilage, ligaments, and other tissues within or around the vertebral column.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus fibrosus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a stretching of the interspinous tissue surrounding the vertebrae. Intervertebral discs mainly function to cushion and tether the vertebrae, while the interspinous tissue including various ligaments, tendons and cartilage, and the like) functions to support the vertebrae so as to provide flexibility and stability to the patient""s spine.
Spinal discs comprise a central hydrostatic cushion, the nucleus pulposus, surrounded by a multi-layered fibrous ligament, the annulus fibrosus. As discs degenerate, they lose their water content and height, bringing the adjoining vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings of the vertebral column which may lead to pinching of the nerve or nerve root. This disc degeneration can eventually cause back and leg pain. Weakness in the annulus from degenerative discs or disc injury can allow fragments of nucleus pulposus to migrate into the annulus fibrosus or spinal canal. There, displaced nucleus fibrosus or protrusion of annulus fibrosus, e.g., herniation, may impinge on spinal nerves. The mere proximity of the nucleus pulposus or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in pain and sensory and motor deficit.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and preventing re-occurrence of the symptoms.
In addition to degenerative discs, many patients have interspinous tissue that has become loose or stretched. Unfortunately, once such tissue has become stretched, it stays stretched. The stretched tissues do not hold the adjacent vertebrae in a stable configuration and allow the vertebrae to separate and xe2x80x9cfloatxe2x80x9d within the vertebral column. The unstable vertebrae can impinge on surrounding nerves and cause the patient pain. Consequently, even if a patient""s discs have been surgically repaired, the patient may still feel pain if there is excessive mobility in their vertebral column.
Until recently, surgical spinal procedures resulted in major operations including traumatic dissection of muscle, and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuing scarring is minimized or completely avoided. In addition, the risk of increased instability due to ligament and bone removal is generally lower in endoscopic procedures than with open procedures. Further, minimally invasive procedures allow more rapid rehabilitation, facilitating faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques, and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (e.g., laparascopic, thoracoscopic,). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments might sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon""s view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage, ligaments, and bone of the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar and bipolar radiofrequency (RF) devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. Monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of undesirable electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large distance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along paths within the patient""s body having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Other disadvantages of conventional RF devices, particularly monopolar devices, is nerve stimulation and interference with nerve monitoring equipment in the operating room. In addition, these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a xe2x80x9ccutting effectxe2x80x9d along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Thus, there is a need for apparatus and methods for electrosurgical treatment of tissues of the vertebral column, wherein damage to tissues in the region of the spine is minimal or non-existent. There is a further need for apparatus and methods for shrinking stretched interspinous tissues, including ligaments, by the controlled direct or indirect application of thermal energy to targeted interspinous tissues, wherein excessive mobility in the vertebral column is decreased and symptoms are alleviated. The instant invention provides such apparatus and methods, as is described in enabling detail hereinbelow.
The present invention provides systems, apparatus, and methods for selectively applying electrical energy to structures within a patient""s body, such as support tissue within or around the spinal column. The systems and methods of the present invention are useful for shrinkage, ablation, resection, aspiration, and/or hemostasis of tissue and other body structures in open and less-invasive spine surgery. In particular, the present invention includes apparatus and methods for the controlled shrinking of interspinous tissue, in which such tissue is treated with thermal energy to cause the tissue to shrink, thereby stiffening the interspinous tissue structure and stabilizing the vertebral column.
In one aspect of the invention, a method is disclosed for treating herniated discs that exhibit progressive instability. In this procedure, the surgeon performs a discectomy with an electrosurgical probe through a small, one to two inch incision in the patient. The surgeon then applies sufficient voltage to the electrode(s) on the probe to shrink the capsule surrounding the posterior facet joints, which enables rotation, thereby tightening the joint, potentially reducing pain, and providing increased stability. This less invasive technique combines the advantages of spine surgery with the traditional clinical benefits of ArthroCare""s Coblation technology (ArthroCare Corporation, Sunnyvale, Calif.). Such clinical benefits include reduced thermal injury, potentially less pain, and faster healing for the patient.
In another aspect, the present invention provides a method of treating interspinous tissue. The method includes positioning one or more active electrode(s) adjacent a target interspinous tissue, and applying high frequency voltage between the active electrode(s) and one or more return electrode(s) to heat and shrink at least a portion of the tissue. The high frequency voltage effects a controlled depth of thermal heating of the tissue to shrink and stiffen the interspinous tissue, thereby at least partially stabilizing the vertebrae and potentially relieving neck or back pain.
In another exemplary embodiment, an electrically conductive media, such as isotonic saline or an electrically conductive gel, is delivered to the target site within the spine to substantially surround the active electrode(s) with the conductive media. The conductive media may be delivered through an instrument to the specific target site, or the entire target region may be filled with conductive media such that the active electrode(s) are submerged during the procedure. Alternatively, the distal end of the instrument may be dipped or otherwise applied to the conductive media prior to introduction into the patient""s body. In all of these embodiments, the electrically conductive media is applied or delivered such that it provides a current flow path between the active and return electrode(s). In other embodiments, electrically conductive fluid naturally present in the patient""s tissue may be used as a substitute for, or as a supplement to, the electrically conductive media that is applied or delivered to the target site
In still another aspect, the present invention provides a method for treating tissue in the vicinity of a facet joint between adjacent vertebrae. The method comprises positioning one or more active electrode(s) adjacent to the tissue in the vicinity of the facet joint. A high frequency voltage difference is applied between the active electrode and a return electrode so as to shrink the tissue in the vicinity of the facet joint thereby stiffening the joint between the adjacent vertebrae. Systems according to the present invention generally include an electrosurgical instrument having a probe or catheter shaft with proximal and distal ends, an electrode assembly at the distal end, and one or more connectors coupling the electrode assembly to a source of high frequency electrical energy. The probe or catheter may assume a wide variety of configurations, with the primary purpose being to introduce the electrode assembly to the patient""s spine (in an open or endoscopic procedure) and to permit the treating physician to manipulate the electrode assembly from a proximal end of the shaft. The electrode assembly includes one or more active electrode(s) configured for tissue ablation and a return electrode spaced from the active electrode(s) either on the instrument shaft or separate from the instrument shaft.
The system further includes a power source coupled to the electrodes on the instrument shaft for applying a high frequency voltage between the active and return electrodes. In one embodiment, the system comprises a voltage reduction element coupled between the power source and active electrode to control the voltage delivered to the active electrode. The voltage reduction element will typically comprise a passive element, such as a capacitor, resistor, inductor, or the like. In the representative embodiment, the power supply can apply a voltage of about 150 volts RMS to 600 volts RMS between the active and return electrodes, but the voltage reduction element will reduce this voltage to about 20 volts RMS to 300 volts RMS to the active electrode. In this manner, the voltage delivered to the active electrode is below the threshold for ablation of tissue, but high enough to sufficiently heat and shrink the tissue.
The active electrode(s) may comprise a single active electrode, or an electrode array, extending from an electrically insulating support member, typically made of a inorganic material such as a ceramic, a polyimide, a silicone rubber, or a glass. The active electrode will usually have a smaller exposed surface area than the return electrode, such that the current densities are much higher at the active electrode than at the return electrode. Preferably, the return electrode has a relatively large, smooth surface extending around the instrument shaft to reduce current densities, thereby minimizing damage to adjacent nontarget tissue.
The apparatus may further include a fluid delivery element for delivering electrically conductive fluid to the active electrode(s) and the target site. The fluid delivery element may be located on the instrument, e.g., a fluid lumen or tube, or it may be part of a separate instrument. Alternatively, an electrically conductive gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the electrode assembly or the target site by other means. In this embodiment, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conductive fluid will preferably generate a current flow path between the active electrode(s) and the return electrode(s).
In another aspect, the present invention provides a method of using an electrosurgical system for treating a defect or disorder of an intervertebral column of a patient, wherein the electrosurgical system includes a power supply coupled to at least one active electrode disposed on a shaft distal end of an electrosurgical probe or catheter. Such defects and disorders include excessive mobility or instability in the vertebral column, which may be associated with excessively loose facet joints between adjacent vertebrae. Excessive mobility or instability of the vertebral column may be due to stretched or loose interspinous tissue, such as various ligaments, which surrounds or lies between the spinous process, the superior articular processes, the inferior articular process, or the transverse processes of the vertebrae. In one aspect, a method for treating the spine involves positioning the shaft distal end such that the at least one active electrode is in the vicinity of the tissue targeted for treatment (interspinous ligament, etc.), and thereafter applying a high frequency voltage between the at least one active electrode and at least one return electrode in a subablation mode, such that the tissue targeted for treatment undergoes shrinkage due to controlled thermal heating. Typically, the controlled heating involves elevating the temperature of the target tissue to a temperature in the range of 45xc2x0 to 90xc2x0 C., more typically 60xc2x0 to 70xc2x0 C. Elevation of the temperature of the targeted tissue within the latter range is particularly suited to effecting shrinkage of collagen fibers of the target tissue. As a result of such treatment, the interspinous tissue shrinks or contracts, typically resulting in increased stability to the spine and concomitant alleviation of symptoms.
In one embodiment, there is provided an electrosurgical system for treating the spine of a patient, the system including a probe having at least one active electrode coupled to a high frequency power supply. The power supply is adapted for applying a suitable high frequency voltage between the at least one active electrode and a return electrode. In one aspect, the system is adapted for toggling between an ablation mode in which a relatively high voltage is applied between the active and return electrodes, and a subablation mode (e.g., thermal heating mode) in which a lower voltage is applied between the active and return electrodes. The subablation mode provides controlled heating of target tissue within a defined temperature range suitable for substantially irreversible shrinkage of target tissue. In one aspect, the system can be readily toggled between the ablation and subablation modes by an operator of the system using a convenient actuator, such as a hand- or foot-operated switch.
In one embodiment, treatment of interspinous tissue to increase stability of the spine may be combined with electrosurgical treatment of a defective intervertebral disc (e.g., ablation, coagulation, or contraction of disc tissue), and/or with an epidural steroid injection. In one embodiment, a method for treating a defective disc or an interspinous tissue involves advancing the shaft distal end of the probe through an introducer needle, with or without an introducer extension tube, towards the target tissue. The use of an introducer needle and introducer extension tube may facilitate positioning the shaft distal end in relation to the tissue targeted for treatment. In one embodiment, the shaft may be positioned, steered, or guided to a target site or tissue under fluoroscopy. Treatment of interspinous tissue according to the invention may be performed in a percutaneous procedure using a posterior lateral approach.
In one aspect, the interspinous tissue may be treated and shrunk using an electrosurgical catheter or probe having a bendable or pre-bent shaft. After introducing the shaft into an appropriate region of the spine, the shaft distal end of such an instrument may be precisely guided to one or more target sites (e.g., interspinous tissue) by a combination of axial translation of the shaft and rotation of the shaft about its longitudinal axis, or by use of pull wires, shape memory actuators, etc. In one aspect of the invention, the shaft distal end may be steered during a surgical procedure so as to adopt a suitable conformation, thereby allowing the shaft distal end to be guided to a target site, for example, to a site between the processes of two adjacent vertebrae. By applying a high frequency voltage between the at least one active electrode and at least one return electrode at a suitable voltage level below the threshold value for ablation (i.e., in a subablation mode), interspinous tissue at the target site undergoes controlled shrinkage. The method may be conveniently performed percutaneously, or alternatively in an open procedure.
For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings.